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been accompanied by gradual infusion of transforming power 
and purpose,, of which physics can take no account,, and to do 
the tasks of which material force has been^ as it were, set as a 
bond- slave. 
Still, however, there will recur the old question, How are 
we to explain the apparent dependence of mental phenomena 
upon material arrangements? A single clot of blood upon 
the brain will destroy consciousness. And how shall we 
account for the phenomena of insanity, and of old age, unless 
we regard the mind as an effect of the material organism ? 
Is it not true, as the German says, Without phosphorus no 
thought ? The argumentative force of these questions depends 
upon the fallacy of which Hume has furnished the refutation 
already quoted. Philosophy does not justify us in asserting that 
the concomitant phenomena of mental and cerebral action are 
related to one another as cause and effect. They are to be 
regarded as conjugate effects of an unknown cause which has 
coupled them together, perhaps only for a time. To say that 
consciousness and thought are 'produced by the motion of the 
molecule of the brain is to outstep the limits of physical 
science, and, more than that, to state a proposition which is 
absolutely inconceivable. To use the language of Professor 
Tyndall, ^‘^it eludes all mental presentation.’^ Vibrations of 
matter cannot be conceived of as translated into thoughts and 
feelings. This would be to cross the unbridgeable chasm 
between mind and matter. And there is this additional 
reason for not regarding the mental as products of the 
accompanying material phenomena. The molecular changes 
in the substance of the living brain result in the generation 
of nervous force. The physical series of events is complete 
in itself, without reference to the synchronous mental series. 
The energy developed in the brain is, no doubt, a physical 
force. As such it can be fully accounted for. It disappears 
in the performance of its appropriate physical work, including 
not only those material phenomena (whatever they may be) 
which accompany thought, but digestion, secretion, respira- 
tion, muscular action ; in short, in the provision of the main 
supply of power for every vital process. We have every 
reason from analogy to believe that the dynamic account of 
expenditure and product could be made out, and exactly 
balanced, were our physiological knowledge equal to the task. 
But in such an account it would not be possible to place 
thought to credit as a product of expended force. The 
account would balance without it. That metaphysical ghost 
the Ego’’ (it is Huxley’s phrase) suddenly looks in on the com- 
pleted calculation of the physicist, as an unwelcome visitant 
